2                       T H E  /proc   F I L E S Y S T E M
   4/proc/sys         Terrehon Bowden <>        October 7 1999
   5                  Bodo Bauer <>
   72.4.x update      Jorge Nerin <>      November 14 2000
   8move /proc/sys    Shen Feng <>                 April 1 2009
  10Version 1.3                                              Kernel version 2.2.12
  11                                              Kernel version 2.4.0-test11-pre4
  13fixes/update part 1.1  Stefani Seibold <>       June 9 2009
  15Table of Contents
  18  0     Preface
  19  0.1   Introduction/Credits
  20  0.2   Legal Stuff
  22  1     Collecting System Information
  23  1.1   Process-Specific Subdirectories
  24  1.2   Kernel data
  25  1.3   IDE devices in /proc/ide
  26  1.4   Networking info in /proc/net
  27  1.5   SCSI info
  28  1.6   Parallel port info in /proc/parport
  29  1.7   TTY info in /proc/tty
  30  1.8   Miscellaneous kernel statistics in /proc/stat
  31  1.9 Ext4 file system parameters
  33  2     Modifying System Parameters
  35  3     Per-Process Parameters
  36  3.1   /proc/<pid>/oom_adj & /proc/<pid>/oom_score_adj - Adjust the oom-killer
  37                                                                score
  38  3.2   /proc/<pid>/oom_score - Display current oom-killer score
  39  3.3   /proc/<pid>/io - Display the IO accounting fields
  40  3.4   /proc/<pid>/coredump_filter - Core dump filtering settings
  41  3.5   /proc/<pid>/mountinfo - Information about mounts
  42  3.6   /proc/<pid>/comm  & /proc/<pid>/task/<tid>/comm
  43  3.7   /proc/<pid>/task/<tid>/children - Information about task children
  44  3.8   /proc/<pid>/fdinfo/<fd> - Information about opened file
  46  4     Configuring procfs
  47  4.1   Mount options
  530.1 Introduction/Credits
  56This documentation is  part of a soon (or  so we hope) to be  released book on
  57the SuSE  Linux distribution. As  there is  no complete documentation  for the
  58/proc file system and we've used  many freely available sources to write these
  59chapters, it  seems only fair  to give the work  back to the  Linux community.
  60This work is  based on the 2.2.*  kernel version and the  upcoming 2.4.*. I'm
  61afraid it's still far from complete, but we  hope it will be useful. As far as
  62we know, it is the first 'all-in-one' document about the /proc file system. It
  63is focused  on the Intel  x86 hardware,  so if you  are looking for  PPC, ARM,
  64SPARC, AXP, etc., features, you probably  won't find what you are looking for.
  65It also only covers IPv4 networking, not IPv6 nor other protocols - sorry. But
  66additions and patches  are welcome and will  be added to this  document if you
  67mail them to Bodo.
  69We'd like  to  thank Alan Cox, Rik van Riel, and Alexey Kuznetsov and a lot of
  70other people for help compiling this documentation. We'd also like to extend a
  71special thank  you to Andi Kleen for documentation, which we relied on heavily
  72to create  this  document,  as well as the additional information he provided.
  73Thanks to  everybody  else  who contributed source or docs to the Linux kernel
  74and helped create a great piece of software... :)
  76If you  have  any comments, corrections or additions, please don't hesitate to
  77contact Bodo  Bauer  at  We'll  be happy to add them to this
  80The   latest   version    of   this   document   is    available   online   at
  83If  the above  direction does  not works  for you,  you could  try the  kernel
  84mailing  list  at  and/or try  to  reach  me  at
  870.2 Legal Stuff
  90We don't  guarantee  the  correctness  of this document, and if you come to us
  91complaining about  how  you  screwed  up  your  system  because  of  incorrect
  92documentation, we won't feel responsible...
  99In This Chapter
 101* Investigating  the  properties  of  the  pseudo  file  system  /proc and its
 102  ability to provide information on the running Linux system
 103* Examining /proc's structure
 104* Uncovering  various  information  about the kernel and the processes running
 105  on the system
 109The proc  file  system acts as an interface to internal data structures in the
 110kernel. It  can  be  used to obtain information about the system and to change
 111certain kernel parameters at runtime (sysctl).
 113First, we'll  take  a  look  at the read-only parts of /proc. In Chapter 2, we
 114show you how you can use /proc/sys to change settings.
 1161.1 Process-Specific Subdirectories
 119The directory  /proc  contains  (among other things) one subdirectory for each
 120process running on the system, which is named after the process ID (PID).
 122The link  self  points  to  the  process reading the file system. Each process
 123subdirectory has the entries listed in Table 1-1.
 126Table 1-1: Process specific entries in /proc
 128 File           Content
 129 clear_refs     Clears page referenced bits shown in smaps output
 130 cmdline        Command line arguments
 131 cpu            Current and last cpu in which it was executed   (2.4)(smp)
 132 cwd            Link to the current working directory
 133 environ        Values of environment variables
 134 exe            Link to the executable of this process
 135 fd             Directory, which contains all file descriptors
 136 maps           Memory maps to executables and library files    (2.4)
 137 mem            Memory held by this process
 138 root           Link to the root directory of this process
 139 stat           Process status
 140 statm          Process memory status information
 141 status         Process status in human readable form
 142 wchan          If CONFIG_KALLSYMS is set, a pre-decoded wchan
 143 pagemap        Page table
 144 stack          Report full stack trace, enable via CONFIG_STACKTRACE
 145 smaps          a extension based on maps, showing the memory consumption of
 146                each mapping and flags associated with it
 149For example, to get the status information of a process, all you have to do is
 150read the file /proc/PID/status:
 152  >cat /proc/self/status
 153  Name:   cat
 154  State:  R (running)
 155  Tgid:   5452
 156  Pid:    5452
 157  PPid:   743
 158  TracerPid:      0                                             (2.4)
 159  Uid:    501     501     501     501
 160  Gid:    100     100     100     100
 161  FDSize: 256
 162  Groups: 100 14 16
 163  VmPeak:     5004 kB
 164  VmSize:     5004 kB
 165  VmLck:         0 kB
 166  VmHWM:       476 kB
 167  VmRSS:       476 kB
 168  VmData:      156 kB
 169  VmStk:        88 kB
 170  VmExe:        68 kB
 171  VmLib:      1412 kB
 172  VmPTE:        20 kb
 173  VmSwap:        0 kB
 174  Threads:        1
 175  SigQ:   0/28578
 176  SigPnd: 0000000000000000
 177  ShdPnd: 0000000000000000
 178  SigBlk: 0000000000000000
 179  SigIgn: 0000000000000000
 180  SigCgt: 0000000000000000
 181  CapInh: 00000000fffffeff
 182  CapPrm: 0000000000000000
 183  CapEff: 0000000000000000
 184  CapBnd: ffffffffffffffff
 185  Seccomp:        0
 186  voluntary_ctxt_switches:        0
 187  nonvoluntary_ctxt_switches:     1
 189This shows you nearly the same information you would get if you viewed it with
 190the ps  command.  In  fact,  ps  uses  the  proc  file  system  to  obtain its
 191information.  But you get a more detailed  view of the  process by reading the
 192file /proc/PID/status. It fields are described in table 1-2.
 194The  statm  file  contains  more  detailed  information about the process
 195memory usage. Its seven fields are explained in Table 1-3.  The stat file
 196contains details information about the process itself.  Its fields are
 197explained in Table 1-4.
 199(for SMP CONFIG users)
 200For making accounting scalable, RSS related information are handled in
 201asynchronous manner and the vaule may not be very precise. To see a precise
 202snapshot of a moment, you can see /proc/<pid>/smaps file and scan page table.
 203It's slow but very precise.
 205Table 1-2: Contents of the status files (as of 2.6.30-rc7)
 207 Field                       Content
 208 Name                        filename of the executable
 209 State                       state (R is running, S is sleeping, D is sleeping
 210                             in an uninterruptible wait, Z is zombie,
 211                             T is traced or stopped)
 212 Tgid                        thread group ID
 213 Pid                         process id
 214 PPid                        process id of the parent process
 215 TracerPid                   PID of process tracing this process (0 if not)
 216 Uid                         Real, effective, saved set, and  file system UIDs
 217 Gid                         Real, effective, saved set, and  file system GIDs
 218 FDSize                      number of file descriptor slots currently allocated
 219 Groups                      supplementary group list
 220 VmPeak                      peak virtual memory size
 221 VmSize                      total program size
 222 VmLck                       locked memory size
 223 VmHWM                       peak resident set size ("high water mark")
 224 VmRSS                       size of memory portions
 225 VmData                      size of data, stack, and text segments
 226 VmStk                       size of data, stack, and text segments
 227 VmExe                       size of text segment
 228 VmLib                       size of shared library code
 229 VmPTE                       size of page table entries
 230 VmSwap                      size of swap usage (the number of referred swapents)
 231 Threads                     number of threads
 232 SigQ                        number of signals queued/max. number for queue
 233 SigPnd                      bitmap of pending signals for the thread
 234 ShdPnd                      bitmap of shared pending signals for the process
 235 SigBlk                      bitmap of blocked signals
 236 SigIgn                      bitmap of ignored signals
 237 SigCgt                      bitmap of caught signals
 238 CapInh                      bitmap of inheritable capabilities
 239 CapPrm                      bitmap of permitted capabilities
 240 CapEff                      bitmap of effective capabilities
 241 CapBnd                      bitmap of capabilities bounding set
 242 Seccomp                     seccomp mode, like prctl(PR_GET_SECCOMP, ...)
 243 Cpus_allowed                mask of CPUs on which this process may run
 244 Cpus_allowed_list           Same as previous, but in "list format"
 245 Mems_allowed                mask of memory nodes allowed to this process
 246 Mems_allowed_list           Same as previous, but in "list format"
 247 voluntary_ctxt_switches     number of voluntary context switches
 248 nonvoluntary_ctxt_switches  number of non voluntary context switches
 251Table 1-3: Contents of the statm files (as of 2.6.8-rc3)
 253 Field    Content
 254 size     total program size (pages)            (same as VmSize in status)
 255 resident size of memory portions (pages)       (same as VmRSS in status)
 256 shared   number of pages that are shared       (i.e. backed by a file)
 257 trs      number of pages that are 'code'       (not including libs; broken,
 258                                                        includes data segment)
 259 lrs      number of pages of library            (always 0 on 2.6)
 260 drs      number of pages of data/stack         (including libs; broken,
 261                                                        includes library text)
 262 dt       number of dirty pages                 (always 0 on 2.6)
 266Table 1-4: Contents of the stat files (as of 2.6.30-rc7)
 268 Field          Content
 269  pid           process id
 270  tcomm         filename of the executable
 271  state         state (R is running, S is sleeping, D is sleeping in an
 272                uninterruptible wait, Z is zombie, T is traced or stopped)
 273  ppid          process id of the parent process
 274  pgrp          pgrp of the process
 275  sid           session id
 276  tty_nr        tty the process uses
 277  tty_pgrp      pgrp of the tty
 278  flags         task flags
 279  min_flt       number of minor faults
 280  cmin_flt      number of minor faults with child's
 281  maj_flt       number of major faults
 282  cmaj_flt      number of major faults with child's
 283  utime         user mode jiffies
 284  stime         kernel mode jiffies
 285  cutime        user mode jiffies with child's
 286  cstime        kernel mode jiffies with child's
 287  priority      priority level
 288  nice          nice level
 289  num_threads   number of threads
 290  it_real_value (obsolete, always 0)
 291  start_time    time the process started after system boot
 292  vsize         virtual memory size
 293  rss           resident set memory size
 294  rsslim        current limit in bytes on the rss
 295  start_code    address above which program text can run
 296  end_code      address below which program text can run
 297  start_stack   address of the start of the main process stack
 298  esp           current value of ESP
 299  eip           current value of EIP
 300  pending       bitmap of pending signals
 301  blocked       bitmap of blocked signals
 302  sigign        bitmap of ignored signals
 303  sigcatch      bitmap of caught signals
 304  wchan         address where process went to sleep
 305  0             (place holder)
 306  0             (place holder)
 307  exit_signal   signal to send to parent thread on exit
 308  task_cpu      which CPU the task is scheduled on
 309  rt_priority   realtime priority
 310  policy        scheduling policy (man sched_setscheduler)
 311  blkio_ticks   time spent waiting for block IO
 312  gtime         guest time of the task in jiffies
 313  cgtime        guest time of the task children in jiffies
 314  start_data    address above which program data+bss is placed
 315  end_data      address below which program data+bss is placed
 316  start_brk     address above which program heap can be expanded with brk()
 317  arg_start     address above which program command line is placed
 318  arg_end       address below which program command line is placed
 319  env_start     address above which program environment is placed
 320  env_end       address below which program environment is placed
 321  exit_code     the thread's exit_code in the form reported by the waitpid system call
 324The /proc/PID/maps file containing the currently mapped memory regions and
 325their access permissions.
 327The format is:
 329address           perms offset  dev   inode      pathname
 33108048000-08049000 r-xp 00000000 03:00 8312       /opt/test
 33208049000-0804a000 rw-p 00001000 03:00 8312       /opt/test
 3330804a000-0806b000 rw-p 00000000 00:00 0          [heap]
 334a7cb1000-a7cb2000 ---p 00000000 00:00 0
 335a7cb2000-a7eb2000 rw-p 00000000 00:00 0
 336a7eb2000-a7eb3000 ---p 00000000 00:00 0
 337a7eb3000-a7ed5000 rw-p 00000000 00:00 0          [stack:1001]
 338a7ed5000-a8008000 r-xp 00000000 03:00 4222       /lib/
 339a8008000-a800a000 r--p 00133000 03:00 4222       /lib/
 340a800a000-a800b000 rw-p 00135000 03:00 4222       /lib/
 341a800b000-a800e000 rw-p 00000000 00:00 0
 342a800e000-a8022000 r-xp 00000000 03:00 14462      /lib/
 343a8022000-a8023000 r--p 00013000 03:00 14462      /lib/
 344a8023000-a8024000 rw-p 00014000 03:00 14462      /lib/
 345a8024000-a8027000 rw-p 00000000 00:00 0
 346a8027000-a8043000 r-xp 00000000 03:00 8317       /lib/
 347a8043000-a8044000 r--p 0001b000 03:00 8317       /lib/
 348a8044000-a8045000 rw-p 0001c000 03:00 8317       /lib/
 349aff35000-aff4a000 rw-p 00000000 00:00 0          [stack]
 350ffffe000-fffff000 r-xp 00000000 00:00 0          [vdso]
 352where "address" is the address space in the process that it occupies, "perms"
 353is a set of permissions:
 355 r = read
 356 w = write
 357 x = execute
 358 s = shared
 359 p = private (copy on write)
 361"offset" is the offset into the mapping, "dev" is the device (major:minor), and
 362"inode" is the inode  on that device.  0 indicates that  no inode is associated
 363with the memory region, as the case would be with BSS (uninitialized data).
 364The "pathname" shows the name associated file for this mapping.  If the mapping
 365is not associated with a file:
 367 [heap]                   = the heap of the program
 368 [stack]                  = the stack of the main process
 369 [stack:1001]             = the stack of the thread with tid 1001
 370 [vdso]                   = the "virtual dynamic shared object",
 371                            the kernel system call handler
 373 or if empty, the mapping is anonymous.
 375The /proc/PID/task/TID/maps is a view of the virtual memory from the viewpoint
 376of the individual tasks of a process. In this file you will see a mapping marked
 377as [stack] if that task sees it as a stack. This is a key difference from the
 378content of /proc/PID/maps, where you will see all mappings that are being used
 379as stack by all of those tasks. Hence, for the example above, the task-level
 380map, i.e. /proc/PID/task/TID/maps for thread 1001 will look like this:
 38208048000-08049000 r-xp 00000000 03:00 8312       /opt/test
 38308049000-0804a000 rw-p 00001000 03:00 8312       /opt/test
 3840804a000-0806b000 rw-p 00000000 00:00 0          [heap]
 385a7cb1000-a7cb2000 ---p 00000000 00:00 0
 386a7cb2000-a7eb2000 rw-p 00000000 00:00 0
 387a7eb2000-a7eb3000 ---p 00000000 00:00 0
 388a7eb3000-a7ed5000 rw-p 00000000 00:00 0          [stack]
 389a7ed5000-a8008000 r-xp 00000000 03:00 4222       /lib/
 390a8008000-a800a000 r--p 00133000 03:00 4222       /lib/
 391a800a000-a800b000 rw-p 00135000 03:00 4222       /lib/
 392a800b000-a800e000 rw-p 00000000 00:00 0
 393a800e000-a8022000 r-xp 00000000 03:00 14462      /lib/
 394a8022000-a8023000 r--p 00013000 03:00 14462      /lib/
 395a8023000-a8024000 rw-p 00014000 03:00 14462      /lib/
 396a8024000-a8027000 rw-p 00000000 00:00 0
 397a8027000-a8043000 r-xp 00000000 03:00 8317       /lib/
 398a8043000-a8044000 r--p 0001b000 03:00 8317       /lib/
 399a8044000-a8045000 rw-p 0001c000 03:00 8317       /lib/
 400aff35000-aff4a000 rw-p 00000000 00:00 0
 401ffffe000-fffff000 r-xp 00000000 00:00 0          [vdso]
 403The /proc/PID/smaps is an extension based on maps, showing the memory
 404consumption for each of the process's mappings. For each of mappings there
 405is a series of lines such as the following:
 40708048000-080bc000 r-xp 00000000 03:02 13130      /bin/bash
 408Size:               1084 kB
 409Rss:                 892 kB
 410Pss:                 374 kB
 411Shared_Clean:        892 kB
 412Shared_Dirty:          0 kB
 413Private_Clean:         0 kB
 414Private_Dirty:         0 kB
 415Referenced:          892 kB
 416Anonymous:             0 kB
 417Swap:                  0 kB
 418KernelPageSize:        4 kB
 419MMUPageSize:           4 kB
 420Locked:              374 kB
 421VmFlags: rd ex mr mw me de
 423the first of these lines shows the same information as is displayed for the
 424mapping in /proc/PID/maps.  The remaining lines show the size of the mapping
 425(size), the amount of the mapping that is currently resident in RAM (RSS), the
 426process' proportional share of this mapping (PSS), the number of clean and
 427dirty private pages in the mapping.  Note that even a page which is part of a
 428MAP_SHARED mapping, but has only a single pte mapped, i.e.  is currently used
 429by only one process, is accounted as private and not as shared.  "Referenced"
 430indicates the amount of memory currently marked as referenced or accessed.
 431"Anonymous" shows the amount of memory that does not belong to any file.  Even
 432a mapping associated with a file may contain anonymous pages: when MAP_PRIVATE
 433and a page is modified, the file page is replaced by a private anonymous copy.
 434"Swap" shows how much would-be-anonymous memory is also used, but out on
 437"VmFlags" field deserves a separate description. This member represents the kernel
 438flags associated with the particular virtual memory area in two letter encoded
 439manner. The codes are the following:
 440    rd  - readable
 441    wr  - writeable
 442    ex  - executable
 443    sh  - shared
 444    mr  - may read
 445    mw  - may write
 446    me  - may execute
 447    ms  - may share
 448    gd  - stack segment growns down
 449    pf  - pure PFN range
 450    dw  - disabled write to the mapped file
 451    lo  - pages are locked in memory
 452    io  - memory mapped I/O area
 453    sr  - sequential read advise provided
 454    rr  - random read advise provided
 455    dc  - do not copy area on fork
 456    de  - do not expand area on remapping
 457    ac  - area is accountable
 458    nr  - swap space is not reserved for the area
 459    ht  - area uses huge tlb pages
 460    nl  - non-linear mapping
 461    ar  - architecture specific flag
 462    dd  - do not include area into core dump
 463    sd  - soft-dirty flag
 464    mm  - mixed map area
 465    hg  - huge page advise flag
 466    nh  - no-huge page advise flag
 467    mg  - mergable advise flag
 469Note that there is no guarantee that every flag and associated mnemonic will
 470be present in all further kernel releases. Things get changed, the flags may
 471be vanished or the reverse -- new added.
 473This file is only present if the CONFIG_MMU kernel configuration option is
 476The /proc/PID/clear_refs is used to reset the PG_Referenced and ACCESSED/YOUNG
 477bits on both physical and virtual pages associated with a process, and the
 478soft-dirty bit on pte (see Documentation/vm/soft-dirty.txt for details).
 479To clear the bits for all the pages associated with the process
 480    > echo 1 > /proc/PID/clear_refs
 482To clear the bits for the anonymous pages associated with the process
 483    > echo 2 > /proc/PID/clear_refs
 485To clear the bits for the file mapped pages associated with the process
 486    > echo 3 > /proc/PID/clear_refs
 488To clear the soft-dirty bit
 489    > echo 4 > /proc/PID/clear_refs
 491Any other value written to /proc/PID/clear_refs will have no effect.
 493The /proc/pid/pagemap gives the PFN, which can be used to find the pageflags
 494using /proc/kpageflags and number of times a page is mapped using
 495/proc/kpagecount. For detailed explanation, see Documentation/vm/pagemap.txt.
 4971.2 Kernel data
 500Similar to  the  process entries, the kernel data files give information about
 501the running kernel. The files used to obtain this information are contained in
 502/proc and  are  listed  in Table 1-5. Not all of these will be present in your
 503system. It  depends  on the kernel configuration and the loaded modules, which
 504files are there, and which are missing.
 506Table 1-5: Kernel info in /proc
 508 File        Content                                           
 509 apm         Advanced power management info                    
 510 buddyinfo   Kernel memory allocator information (see text)     (2.5)
 511 bus         Directory containing bus specific information     
 512 cmdline     Kernel command line                               
 513 cpuinfo     Info about the CPU                                
 514 devices     Available devices (block and character)           
 515 dma         Used DMS channels                                 
 516 filesystems Supported filesystems                             
 517 driver      Various drivers grouped here, currently rtc (2.4)
 518 execdomains Execdomains, related to security                   (2.4)
 519 fb          Frame Buffer devices                               (2.4)
 520 fs          File system parameters, currently nfs/exports      (2.4)
 521 ide         Directory containing info about the IDE subsystem 
 522 interrupts  Interrupt usage                                   
 523 iomem       Memory map                                         (2.4)
 524 ioports     I/O port usage                                    
 525 irq         Masks for irq to cpu affinity                      (2.4)(smp?)
 526 isapnp      ISA PnP (Plug&Play) Info                           (2.4)
 527 kcore       Kernel core image (can be ELF or A.OUT(deprecated in 2.4))   
 528 kmsg        Kernel messages                                   
 529 ksyms       Kernel symbol table                               
 530 loadavg     Load average of last 1, 5 & 15 minutes                
 531 locks       Kernel locks                                      
 532 meminfo     Memory info                                       
 533 misc        Miscellaneous                                     
 534 modules     List of loaded modules                            
 535 mounts      Mounted filesystems                               
 536 net         Networking info (see text)                        
 537 pagetypeinfo Additional page allocator information (see text)  (2.5)
 538 partitions  Table of partitions known to the system           
 539 pci         Deprecated info of PCI bus (new way -> /proc/bus/pci/,
 540             decoupled by lspci                                 (2.4)
 541 rtc         Real time clock                                   
 542 scsi        SCSI info (see text)                              
 543 slabinfo    Slab pool info                                    
 544 softirqs    softirq usage
 545 stat        Overall statistics                                
 546 swaps       Swap space utilization                            
 547 sys         See chapter 2                                     
 548 sysvipc     Info of SysVIPC Resources (msg, sem, shm)          (2.4)
 549 tty         Info of tty drivers
 550 uptime      Wall clock since boot, combined idle time of all cpus
 551 version     Kernel version                                    
 552 video       bttv info of video resources                       (2.4)
 553 vmallocinfo Show vmalloced areas
 556You can,  for  example,  check  which interrupts are currently in use and what
 557they are used for by looking in the file /proc/interrupts:
 559  > cat /proc/interrupts 
 560             CPU0        
 561    0:    8728810          XT-PIC  timer 
 562    1:        895          XT-PIC  keyboard 
 563    2:          0          XT-PIC  cascade 
 564    3:     531695          XT-PIC  aha152x 
 565    4:    2014133          XT-PIC  serial 
 566    5:      44401          XT-PIC  pcnet_cs 
 567    8:          2          XT-PIC  rtc 
 568   11:          8          XT-PIC  i82365 
 569   12:     182918          XT-PIC  PS/2 Mouse 
 570   13:          1          XT-PIC  fpu 
 571   14:    1232265          XT-PIC  ide0 
 572   15:          7          XT-PIC  ide1 
 573  NMI:          0 
 575In 2.4.* a couple of lines where added to this file LOC & ERR (this time is the
 576output of a SMP machine):
 578  > cat /proc/interrupts 
 580             CPU0       CPU1       
 581    0:    1243498    1214548    IO-APIC-edge  timer
 582    1:       8949       8958    IO-APIC-edge  keyboard
 583    2:          0          0          XT-PIC  cascade
 584    5:      11286      10161    IO-APIC-edge  soundblaster
 585    8:          1          0    IO-APIC-edge  rtc
 586    9:      27422      27407    IO-APIC-edge  3c503
 587   12:     113645     113873    IO-APIC-edge  PS/2 Mouse
 588   13:          0          0          XT-PIC  fpu
 589   14:      22491      24012    IO-APIC-edge  ide0
 590   15:       2183       2415    IO-APIC-edge  ide1
 591   17:      30564      30414   IO-APIC-level  eth0
 592   18:        177        164   IO-APIC-level  bttv
 593  NMI:    2457961    2457959 
 594  LOC:    2457882    2457881 
 595  ERR:       2155
 597NMI is incremented in this case because every timer interrupt generates a NMI
 598(Non Maskable Interrupt) which is used by the NMI Watchdog to detect lockups.
 600LOC is the local interrupt counter of the internal APIC of every CPU.
 602ERR is incremented in the case of errors in the IO-APIC bus (the bus that
 603connects the CPUs in a SMP system. This means that an error has been detected,
 604the IO-APIC automatically retry the transmission, so it should not be a big
 605problem, but you should read the SMP-FAQ.
 607In 2.6.2* /proc/interrupts was expanded again.  This time the goal was for
 608/proc/interrupts to display every IRQ vector in use by the system, not
 609just those considered 'most important'.  The new vectors are:
 611  THR -- interrupt raised when a machine check threshold counter
 612  (typically counting ECC corrected errors of memory or cache) exceeds
 613  a configurable threshold.  Only available on some systems.
 615  TRM -- a thermal event interrupt occurs when a temperature threshold
 616  has been exceeded for the CPU.  This interrupt may also be generated
 617  when the temperature drops back to normal.
 619  SPU -- a spurious interrupt is some interrupt that was raised then lowered
 620  by some IO device before it could be fully processed by the APIC.  Hence
 621  the APIC sees the interrupt but does not know what device it came from.
 622  For this case the APIC will generate the interrupt with a IRQ vector
 623  of 0xff. This might also be generated by chipset bugs.
 625  RES, CAL, TLB -- rescheduling, call and TLB flush interrupts are
 626  sent from one CPU to another per the needs of the OS.  Typically,
 627  their statistics are used by kernel developers and interested users to
 628  determine the occurrence of interrupts of the given type.
 630The above IRQ vectors are displayed only when relevant.  For example,
 631the threshold vector does not exist on x86_64 platforms.  Others are
 632suppressed when the system is a uniprocessor.  As of this writing, only
 633i386 and x86_64 platforms support the new IRQ vector displays.
 635Of some interest is the introduction of the /proc/irq directory to 2.4.
 636It could be used to set IRQ to CPU affinity, this means that you can "hook" an
 637IRQ to only one CPU, or to exclude a CPU of handling IRQs. The contents of the
 638irq subdir is one subdir for each IRQ, and two files; default_smp_affinity and
 641For example 
 642  > ls /proc/irq/
 643  0  10  12  14  16  18  2  4  6  8  prof_cpu_mask
 644  1  11  13  15  17  19  3  5  7  9  default_smp_affinity
 645  > ls /proc/irq/0/
 646  smp_affinity
 648smp_affinity is a bitmask, in which you can specify which CPUs can handle the
 649IRQ, you can set it by doing:
 651  > echo 1 > /proc/irq/10/smp_affinity
 653This means that only the first CPU will handle the IRQ, but you can also echo
 6545 which means that only the first and fourth CPU can handle the IRQ.
 656The contents of each smp_affinity file is the same by default:
 658  > cat /proc/irq/0/smp_affinity
 659  ffffffff
 661There is an alternate interface, smp_affinity_list which allows specifying
 662a cpu range instead of a bitmask:
 664  > cat /proc/irq/0/smp_affinity_list
 665  1024-1031
 667The default_smp_affinity mask applies to all non-active IRQs, which are the
 668IRQs which have not yet been allocated/activated, and hence which lack a
 669/proc/irq/[0-9]* directory.
 671The node file on an SMP system shows the node to which the device using the IRQ
 672reports itself as being attached. This hardware locality information does not
 673include information about any possible driver locality preference.
 675prof_cpu_mask specifies which CPUs are to be profiled by the system wide
 676profiler. Default value is ffffffff (all cpus if there are only 32 of them).
 678The way IRQs are routed is handled by the IO-APIC, and it's Round Robin
 679between all the CPUs which are allowed to handle it. As usual the kernel has
 680more info than you and does a better job than you, so the defaults are the
 681best choice for almost everyone.  [Note this applies only to those IO-APIC's
 682that support "Round Robin" interrupt distribution.]
 684There are  three  more  important subdirectories in /proc: net, scsi, and sys.
 685The general  rule  is  that  the  contents,  or  even  the  existence of these
 686directories, depend  on your kernel configuration. If SCSI is not enabled, the
 687directory scsi  may  not  exist. The same is true with the net, which is there
 688only when networking support is present in the running kernel.
 690The slabinfo  file  gives  information  about  memory usage at the slab level.
 691Linux uses  slab  pools for memory management above page level in version 2.2.
 692Commonly used  objects  have  their  own  slab  pool (such as network buffers,
 693directory cache, and so on).
 697> cat /proc/buddyinfo
 699Node 0, zone      DMA      0      4      5      4      4      3 ...
 700Node 0, zone   Normal      1      0      0      1    101      8 ...
 701Node 0, zone  HighMem      2      0      0      1      1      0 ...
 703External fragmentation is a problem under some workloads, and buddyinfo is a
 704useful tool for helping diagnose these problems.  Buddyinfo will give you a 
 705clue as to how big an area you can safely allocate, or why a previous
 706allocation failed.
 708Each column represents the number of pages of a certain order which are 
 709available.  In this case, there are 0 chunks of 2^0*PAGE_SIZE available in 
 710ZONE_DMA, 4 chunks of 2^1*PAGE_SIZE in ZONE_DMA, 101 chunks of 2^4*PAGE_SIZE 
 711available in ZONE_NORMAL, etc... 
 713More information relevant to external fragmentation can be found in
 716> cat /proc/pagetypeinfo
 717Page block order: 9
 718Pages per block:  512
 720Free pages count per migrate type at order       0      1      2      3      4      5      6      7      8      9     10
 721Node    0, zone      DMA, type    Unmovable      0      0      0      1      1      1      1      1      1      1      0
 722Node    0, zone      DMA, type  Reclaimable      0      0      0      0      0      0      0      0      0      0      0
 723Node    0, zone      DMA, type      Movable      1      1      2      1      2      1      1      0      1      0      2
 724Node    0, zone      DMA, type      Reserve      0      0      0      0      0      0      0      0      0      1      0
 725Node    0, zone      DMA, type      Isolate      0      0      0      0      0      0      0      0      0      0      0
 726Node    0, zone    DMA32, type    Unmovable    103     54     77      1      1      1     11      8      7      1      9
 727Node    0, zone    DMA32, type  Reclaimable      0      0      2      1      0      0      0      0      1      0      0
 728Node    0, zone    DMA32, type      Movable    169    152    113     91     77     54     39     13      6      1    452
 729Node    0, zone    DMA32, type      Reserve      1      2      2      2      2      0      1      1      1      1      0
 730Node    0, zone    DMA32, type      Isolate      0      0      0      0      0      0      0      0      0      0      0
 732Number of blocks type     Unmovable  Reclaimable      Movable      Reserve      Isolate
 733Node 0, zone      DMA            2            0            5            1            0
 734Node 0, zone    DMA32           41            6          967            2            0
 736Fragmentation avoidance in the kernel works by grouping pages of different
 737migrate types into the same contiguous regions of memory called page blocks.
 738A page block is typically the size of the default hugepage size e.g. 2MB on
 739X86-64. By keeping pages grouped based on their ability to move, the kernel
 740can reclaim pages within a page block to satisfy a high-order allocation.
 742The pagetypinfo begins with information on the size of a page block. It
 743then gives the same type of information as buddyinfo except broken down
 744by migrate-type and finishes with details on how many page blocks of each
 745type exist.
 747If min_free_kbytes has been tuned correctly (recommendations made by hugeadm
 748from libhugetlbfs, one can
 749make an estimate of the likely number of huge pages that can be allocated
 750at a given point in time. All the "Movable" blocks should be allocatable
 751unless memory has been mlock()'d. Some of the Reclaimable blocks should
 752also be allocatable although a lot of filesystem metadata may have to be
 753reclaimed to achieve this.
 759Provides information about distribution and utilization of memory.  This
 760varies by architecture and compile options.  The following is from a
 76116GB PIII, which has highmem enabled.  You may not have all of these fields.
 763> cat /proc/meminfo
 765The "Locked" indicates whether the mapping is locked in memory or not.
 768MemTotal:     16344972 kB
 769MemFree:      13634064 kB
 770MemAvailable: 14836172 kB
 771Buffers:          3656 kB
 772Cached:        1195708 kB
 773SwapCached:          0 kB
 774Active:         891636 kB
 775Inactive:      1077224 kB
 776HighTotal:    15597528 kB
 777HighFree:     13629632 kB
 778LowTotal:       747444 kB
 779LowFree:          4432 kB
 780SwapTotal:           0 kB
 781SwapFree:            0 kB
 782Dirty:             968 kB
 783Writeback:           0 kB
 784AnonPages:      861800 kB
 785Mapped:         280372 kB
 786Slab:           284364 kB
 787SReclaimable:   159856 kB
 788SUnreclaim:     124508 kB
 789PageTables:      24448 kB
 790NFS_Unstable:        0 kB
 791Bounce:              0 kB
 792WritebackTmp:        0 kB
 793CommitLimit:   7669796 kB
 794Committed_AS:   100056 kB
 795VmallocTotal:   112216 kB
 796VmallocUsed:       428 kB
 797VmallocChunk:   111088 kB
 798AnonHugePages:   49152 kB
 800    MemTotal: Total usable ram (i.e. physical ram minus a few reserved
 801              bits and the kernel binary code)
 802     MemFree: The sum of LowFree+HighFree
 803MemAvailable: An estimate of how much memory is available for starting new
 804              applications, without swapping. Calculated from MemFree,
 805              SReclaimable, the size of the file LRU lists, and the low
 806              watermarks in each zone.
 807              The estimate takes into account that the system needs some
 808              page cache to function well, and that not all reclaimable
 809              slab will be reclaimable, due to items being in use. The
 810              impact of those factors will vary from system to system.
 811     Buffers: Relatively temporary storage for raw disk blocks
 812              shouldn't get tremendously large (20MB or so)
 813      Cached: in-memory cache for files read from the disk (the
 814              pagecache).  Doesn't include SwapCached
 815  SwapCached: Memory that once was swapped out, is swapped back in but
 816              still also is in the swapfile (if memory is needed it
 817              doesn't need to be swapped out AGAIN because it is already
 818              in the swapfile. This saves I/O)
 819      Active: Memory that has been used more recently and usually not
 820              reclaimed unless absolutely necessary.
 821    Inactive: Memory which has been less recently used.  It is more
 822              eligible to be reclaimed for other purposes
 823   HighTotal:
 824    HighFree: Highmem is all memory above ~860MB of physical memory
 825              Highmem areas are for use by userspace programs, or
 826              for the pagecache.  The kernel must use tricks to access
 827              this memory, making it slower to access than lowmem.
 828    LowTotal:
 829     LowFree: Lowmem is memory which can be used for everything that
 830              highmem can be used for, but it is also available for the
 831              kernel's use for its own data structures.  Among many
 832              other things, it is where everything from the Slab is
 833              allocated.  Bad things happen when you're out of lowmem.
 834   SwapTotal: total amount of swap space available
 835    SwapFree: Memory which has been evicted from RAM, and is temporarily
 836              on the disk
 837       Dirty: Memory which is waiting to get written back to the disk
 838   Writeback: Memory which is actively being written back to the disk
 839   AnonPages: Non-file backed pages mapped into userspace page tables
 840AnonHugePages: Non-file backed huge pages mapped into userspace page tables
 841      Mapped: files which have been mmaped, such as libraries
 842        Slab: in-kernel data structures cache
 843SReclaimable: Part of Slab, that might be reclaimed, such as caches
 844  SUnreclaim: Part of Slab, that cannot be reclaimed on memory pressure
 845  PageTables: amount of memory dedicated to the lowest level of page
 846              tables.
 847NFS_Unstable: NFS pages sent to the server, but not yet committed to stable
 848              storage
 849      Bounce: Memory used for block device "bounce buffers"
 850WritebackTmp: Memory used by FUSE for temporary writeback buffers
 851 CommitLimit: Based on the overcommit ratio ('vm.overcommit_ratio'),
 852              this is the total amount of  memory currently available to
 853              be allocated on the system. This limit is only adhered to
 854              if strict overcommit accounting is enabled (mode 2 in
 855              'vm.overcommit_memory').
 856              The CommitLimit is calculated with the following formula:
 857              CommitLimit = ([total RAM pages] - [total huge TLB pages]) *
 858                             overcommit_ratio / 100 + [total swap pages]
 859              For example, on a system with 1G of physical RAM and 7G
 860              of swap with a `vm.overcommit_ratio` of 30 it would
 861              yield a CommitLimit of 7.3G.
 862              For more details, see the memory overcommit documentation
 863              in vm/overcommit-accounting.
 864Committed_AS: The amount of memory presently allocated on the system.
 865              The committed memory is a sum of all of the memory which
 866              has been allocated by processes, even if it has not been
 867              "used" by them as of yet. A process which malloc()'s 1G
 868              of memory, but only touches 300M of it will show up as
 869              using 1G. This 1G is memory which has been "committed" to
 870              by the VM and can be used at any time by the allocating
 871              application. With strict overcommit enabled on the system
 872              (mode 2 in 'vm.overcommit_memory'),allocations which would
 873              exceed the CommitLimit (detailed above) will not be permitted.
 874              This is useful if one needs to guarantee that processes will
 875              not fail due to lack of memory once that memory has been
 876              successfully allocated.
 877VmallocTotal: total size of vmalloc memory area
 878 VmallocUsed: amount of vmalloc area which is used
 879VmallocChunk: largest contiguous block of vmalloc area which is free
 885Provides information about vmalloced/vmaped areas. One line per area,
 886containing the virtual address range of the area, size in bytes,
 887caller information of the creator, and optional information depending
 888on the kind of area :
 890 pages=nr    number of pages
 891 phys=addr   if a physical address was specified
 892 ioremap     I/O mapping (ioremap() and friends)
 893 vmalloc     vmalloc() area
 894 vmap        vmap()ed pages
 895 user        VM_USERMAP area
 896 vpages      buffer for pages pointers was vmalloced (huge area)
 897 N<node>=nr  (Only on NUMA kernels)
 898             Number of pages allocated on memory node <node>
 900> cat /proc/vmallocinfo
 9010xffffc20000000000-0xffffc20000201000 2101248 alloc_large_system_hash+0x204 ...
 902  /0x2c0 pages=512 vmalloc N0=128 N1=128 N2=128 N3=128
 9030xffffc20000201000-0xffffc20000302000 1052672 alloc_large_system_hash+0x204 ...
 904  /0x2c0 pages=256 vmalloc N0=64 N1=64 N2=64 N3=64
 9050xffffc20000302000-0xffffc20000304000    8192 acpi_tb_verify_table+0x21/0x4f...
 906  phys=7fee8000 ioremap
 9070xffffc20000304000-0xffffc20000307000   12288 acpi_tb_verify_table+0x21/0x4f...
 908  phys=7fee7000 ioremap
 9090xffffc2000031d000-0xffffc2000031f000    8192 init_vdso_vars+0x112/0x210
 9100xffffc2000031f000-0xffffc2000032b000   49152 cramfs_uncompress_init+0x2e ...
 911  /0x80 pages=11 vmalloc N0=3 N1=3 N2=2 N3=3
 9120xffffc2000033a000-0xffffc2000033d000   12288 sys_swapon+0x640/0xac0      ...
 913  pages=2 vmalloc N1=2
 9140xffffc20000347000-0xffffc2000034c000   20480 xt_alloc_table_info+0xfe ...
 915  /0x130 [x_tables] pages=4 vmalloc N0=4
 9160xffffffffa0000000-0xffffffffa000f000   61440 sys_init_module+0xc27/0x1d00 ...
 917   pages=14 vmalloc N2=14
 9180xffffffffa000f000-0xffffffffa0014000   20480 sys_init_module+0xc27/0x1d00 ...
 919   pages=4 vmalloc N1=4
 9200xffffffffa0014000-0xffffffffa0017000   12288 sys_init_module+0xc27/0x1d00 ...
 921   pages=2 vmalloc N1=2
 9220xffffffffa0017000-0xffffffffa0022000   45056 sys_init_module+0xc27/0x1d00 ...
 923   pages=10 vmalloc N0=10
 929Provides counts of softirq handlers serviced since boot time, for each cpu.
 931> cat /proc/softirqs
 932                CPU0       CPU1       CPU2       CPU3
 933      HI:          0          0          0          0
 934   TIMER:      27166      27120      27097      27034
 935  NET_TX:          0          0          0         17
 936  NET_RX:         42          0          0         39
 937   BLOCK:          0          0        107       1121
 938 TASKLET:          0          0          0        290
 939   SCHED:      27035      26983      26971      26746
 940 HRTIMER:          0          0          0          0
 941     RCU:       1678       1769       2178       2250
 9441.3 IDE devices in /proc/ide
 947The subdirectory /proc/ide contains information about all IDE devices of which
 948the kernel  is  aware.  There is one subdirectory for each IDE controller, the
 949file drivers  and a link for each IDE device, pointing to the device directory
 950in the controller specific subtree.
 952The file  drivers  contains general information about the drivers used for the
 953IDE devices:
 955  > cat /proc/ide/drivers
 956  ide-cdrom version 4.53
 957  ide-disk version 1.08
 959More detailed  information  can  be  found  in  the  controller  specific
 960subdirectories. These  are  named  ide0,  ide1  and  so  on.  Each  of  these
 961directories contains the files shown in table 1-6.
 964Table 1-6: IDE controller info in  /proc/ide/ide?
 966 File    Content                                 
 967 channel IDE channel (0 or 1)                    
 968 config  Configuration (only for PCI/IDE bridge) 
 969 mate    Mate name                               
 970 model   Type/Chipset of IDE controller          
 973Each device  connected  to  a  controller  has  a separate subdirectory in the
 974controllers directory.  The  files  listed in table 1-7 are contained in these
 978Table 1-7: IDE device information
 980 File             Content                                    
 981 cache            The cache                                  
 982 capacity         Capacity of the medium (in 512Byte blocks) 
 983 driver           driver and version                         
 984 geometry         physical and logical geometry              
 985 identify         device identify block                      
 986 media            media type                                 
 987 model            device identifier                          
 988 settings         device setup                               
 989 smart_thresholds IDE disk management thresholds             
 990 smart_values     IDE disk management values                 
 993The most  interesting  file is settings. This file contains a nice overview of
 994the drive parameters:
 996  # cat /proc/ide/ide0/hda/settings 
 997  name                    value           min             max             mode 
 998  ----                    -----           ---             ---             ---- 
 999  bios_cyl                526             0               65535           rw 
1000  bios_head               255             0               255             rw 
1001  bios_sect               63              0               63              rw 
1002  breada_readahead        4               0               127             rw 
1003  bswap                   0               0               1               r 
1004  file_readahead          72              0               2097151         rw 
1005  io_32bit                0               0               3               rw 
1006  keepsettings            0               0               1               rw 
1007  max_kb_per_request      122             1               127             rw 
1008  multcount               0               0               8               rw 
1009  nice1                   1               0               1               rw 
1010  nowerr                  0               0               1               rw 
1011  pio_mode                write-only      0               255             w 
1012  slow                    0               0               1               rw 
1013  unmaskirq               0               0               1               rw 
1014  using_dma               0               0               1               rw 
10171.4 Networking info in /proc/net
1020The subdirectory  /proc/net  follows  the  usual  pattern. Table 1-8 shows the
1021additional values  you  get  for  IP  version 6 if you configure the kernel to
1022support this. Table 1-9 lists the files and their meaning.
1025Table 1-8: IPv6 info in /proc/net
1027 File       Content                                               
1028 udp6       UDP sockets (IPv6)                                    
1029 tcp6       TCP sockets (IPv6)                                    
1030 raw6       Raw device statistics (IPv6)                          
1031 igmp6      IP multicast addresses, which this host joined (IPv6) 
1032 if_inet6   List of IPv6 interface addresses                      
1033 ipv6_route Kernel routing table for IPv6                         
1034 rt6_stats  Global IPv6 routing tables statistics                 
1035 sockstat6  Socket statistics (IPv6)                              
1036 snmp6      Snmp data (IPv6)                                      
1040Table 1-9: Network info in /proc/net
1042 File          Content                                                         
1043 arp           Kernel  ARP table                                               
1044 dev           network devices with statistics                                 
1045 dev_mcast     the Layer2 multicast groups a device is listening too
1046               (interface index, label, number of references, number of bound
1047               addresses). 
1048 dev_stat      network device status                                           
1049 ip_fwchains   Firewall chain linkage                                          
1050 ip_fwnames    Firewall chain names                                            
1051 ip_masq       Directory containing the masquerading tables                    
1052 ip_masquerade Major masquerading table                                        
1053 netstat       Network statistics                                              
1054 raw           raw device statistics                                           
1055 route         Kernel routing table                                            
1056 rpc           Directory containing rpc info                                   
1057 rt_cache      Routing cache                                                   
1058 snmp          SNMP data                                                       
1059 sockstat      Socket statistics                                               
1060 tcp           TCP  sockets                                                    
1061 udp           UDP sockets                                                     
1062 unix          UNIX domain sockets                                             
1063 wireless      Wireless interface data (Wavelan etc)                           
1064 igmp          IP multicast addresses, which this host joined                  
1065 psched        Global packet scheduler parameters.                             
1066 netlink       List of PF_NETLINK sockets                                      
1067 ip_mr_vifs    List of multicast virtual interfaces                            
1068 ip_mr_cache   List of multicast routing cache                                 
1071You can  use  this  information  to see which network devices are available in
1072your system and how much traffic was routed over those devices:
1074  > cat /proc/net/dev 
1075  Inter-|Receive                                                   |[... 
1076   face |bytes    packets errs drop fifo frame compressed multicast|[... 
1077      lo:  908188   5596     0    0    0     0          0         0 [...         
1078    ppp0:15475140  20721   410    0    0   410          0         0 [...  
1079    eth0:  614530   7085     0    0    0     0          0         1 [... 
1081  ...] Transmit 
1082  ...] bytes    packets errs drop fifo colls carrier compressed 
1083  ...]  908188     5596    0    0    0     0       0          0 
1084  ...] 1375103    17405    0    0    0     0       0          0 
1085  ...] 1703981     5535    0    0    0     3       0          0 
1087In addition, each Channel Bond interface has its own directory.  For
1088example, the bond0 device will have a directory called /proc/net/bond0/.
1089It will contain information that is specific to that bond, such as the
1090current slaves of the bond, the link status of the slaves, and how
1091many times the slaves link has failed.
10931.5 SCSI info
1096If you  have  a  SCSI  host adapter in your system, you'll find a subdirectory
1097named after  the driver for this adapter in /proc/scsi. You'll also see a list
1098of all recognized SCSI devices in /proc/scsi:
1100  >cat /proc/scsi/scsi 
1101  Attached devices: 
1102  Host: scsi0 Channel: 00 Id: 00 Lun: 00 
1103    Vendor: IBM      Model: DGHS09U          Rev: 03E0 
1104    Type:   Direct-Access                    ANSI SCSI revision: 03 
1105  Host: scsi0 Channel: 00 Id: 06 Lun: 00 
1106    Vendor: PIONEER  Model: CD-ROM DR-U06S   Rev: 1.04 
1107    Type:   CD-ROM                           ANSI SCSI revision: 02 
1110The directory  named  after  the driver has one file for each adapter found in
1111the system.  These  files  contain information about the controller, including
1112the used  IRQ  and  the  IO  address range. The amount of information shown is
1113dependent on  the adapter you use. The example shows the output for an Adaptec
1114AHA-2940 SCSI adapter:
1116  > cat /proc/scsi/aic7xxx/0 
1118  Adaptec AIC7xxx driver version: 5.1.19/3.2.4 
1119  Compile Options: 
1120    TCQ Enabled By Default : Disabled 
1121    AIC7XXX_PROC_STATS     : Disabled 
1122    AIC7XXX_RESET_DELAY    : 5 
1123  Adapter Configuration: 
1124             SCSI Adapter: Adaptec AHA-294X Ultra SCSI host adapter 
1125                             Ultra Wide Controller 
1126      PCI MMAPed I/O Base: 0xeb001000 
1127   Adapter SEEPROM Config: SEEPROM found and used. 
1128        Adaptec SCSI BIOS: Enabled 
1129                      IRQ: 10 
1130                     SCBs: Active 0, Max Active 2, 
1131                           Allocated 15, HW 16, Page 255 
1132               Interrupts: 160328 
1133        BIOS Control Word: 0x18b6 
1134     Adapter Control Word: 0x005b 
1135     Extended Translation: Enabled 
1136  Disconnect Enable Flags: 0xffff 
1137       Ultra Enable Flags: 0x0001 
1138   Tag Queue Enable Flags: 0x0000 
1139  Ordered Queue Tag Flags: 0x0000 
1140  Default Tag Queue Depth: 8 
1141      Tagged Queue By Device array for aic7xxx host instance 0: 
1142        {255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255} 
1143      Actual queue depth per device for aic7xxx host instance 0: 
1144        {1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1} 
1145  Statistics: 
1146  (scsi0:0:0:0) 
1147    Device using Wide/Sync transfers at 40.0 MByte/sec, offset 8 
1148    Transinfo settings: current(12/8/1/0), goal(12/8/1/0), user(12/15/1/0) 
1149    Total transfers 160151 (74577 reads and 85574 writes) 
1150  (scsi0:0:6:0) 
1151    Device using Narrow/Sync transfers at 5.0 MByte/sec, offset 15 
1152    Transinfo settings: current(50/15/0/0), goal(50/15/0/0), user(50/15/0/0) 
1153    Total transfers 0 (0 reads and 0 writes) 
11561.6 Parallel port info in /proc/parport
1159The directory  /proc/parport  contains information about the parallel ports of
1160your system.  It  has  one  subdirectory  for  each port, named after the port
1161number (0,1,2,...).
1163These directories contain the four files shown in Table 1-10.
1166Table 1-10: Files in /proc/parport
1168 File      Content                                                             
1169 autoprobe Any IEEE-1284 device ID information that has been acquired.         
1170 devices   list of the device drivers using that port. A + will appear by the
1171           name of the device currently using the port (it might not appear
1172           against any). 
1173 hardware  Parallel port's base address, IRQ line and DMA channel.             
1174 irq       IRQ that parport is using for that port. This is in a separate
1175           file to allow you to alter it by writing a new value in (IRQ
1176           number or none). 
11791.7 TTY info in /proc/tty
1182Information about  the  available  and actually used tty's can be found in the
1183directory /proc/tty.You'll  find  entries  for drivers and line disciplines in
1184this directory, as shown in Table 1-11.
1187Table 1-11: Files in /proc/tty
1189 File          Content                                        
1190 drivers       list of drivers and their usage                
1191 ldiscs        registered line disciplines                    
1192 driver/serial usage statistic and status of single tty lines 
1195To see  which  tty's  are  currently in use, you can simply look into the file
1198  > cat /proc/tty/drivers 
1199  pty_slave            /dev/pts      136   0-255 pty:slave 
1200  pty_master           /dev/ptm      128   0-255 pty:master 
1201  pty_slave            /dev/ttyp       3   0-255 pty:slave 
1202  pty_master           /dev/pty        2   0-255 pty:master 
1203  serial               /dev/cua        5   64-67 serial:callout 
1204  serial               /dev/ttyS       4   64-67 serial 
1205  /dev/tty0            /dev/tty0       4       0 system:vtmaster 
1206  /dev/ptmx            /dev/ptmx       5       2 system 
1207  /dev/console         /dev/console    5       1 system:console 
1208  /dev/tty             /dev/tty        5       0 system:/dev/tty 
1209  unknown              /dev/tty        4    1-63 console 
12121.8 Miscellaneous kernel statistics in /proc/stat
1215Various pieces   of  information about  kernel activity  are  available in the
1216/proc/stat file.  All  of  the numbers reported  in  this file are  aggregates
1217since the system first booted.  For a quick look, simply cat the file:
1219  > cat /proc/stat
1220  cpu  2255 34 2290 22625563 6290 127 456 0 0
1221  cpu0 1132 34 1441 11311718 3675 127 438 0 0
1222  cpu1 1123 0 849 11313845 2614 0 18 0 0
1223  intr 114930548 113199788 3 0 5 263 0 4 [... lots more numbers ...]
1224  ctxt 1990473
1225  btime 1062191376
1226  processes 2915
1227  procs_running 1
1228  procs_blocked 0
1229  softirq 183433 0 21755 12 39 1137 231 21459 2263
1231The very first  "cpu" line aggregates the  numbers in all  of the other "cpuN"
1232lines.  These numbers identify the amount of time the CPU has spent performing
1233different kinds of work.  Time units are in USER_HZ (typically hundredths of a
1234second).  The meanings of the columns are as follows, from left to right:
1236- user: normal processes executing in user mode
1237- nice: niced processes executing in user mode
1238- system: processes executing in kernel mode
1239- idle: twiddling thumbs
1240- iowait: waiting for I/O to complete
1241- irq: servicing interrupts
1242- softirq: servicing softirqs
1243- steal: involuntary wait
1244- guest: running a normal guest
1245- guest_nice: running a niced guest
1247The "intr" line gives counts of interrupts  serviced since boot time, for each
1248of the  possible system interrupts.   The first  column  is the  total of  all
1249interrupts serviced  including  unnumbered  architecture specific  interrupts;
1250each  subsequent column is the  total for that particular numbered interrupt.
1251Unnumbered interrupts are not shown, only summed into the total.
1253The "ctxt" line gives the total number of context switches across all CPUs.
1255The "btime" line gives  the time at which the  system booted, in seconds since
1256the Unix epoch.
1258The "processes" line gives the number  of processes and threads created, which
1259includes (but  is not limited  to) those  created by  calls to the  fork() and
1260clone() system calls.
1262The "procs_running" line gives the total number of threads that are
1263running or ready to run (i.e., the total number of runnable threads).
1265The   "procs_blocked" line gives  the  number of  processes currently blocked,
1266waiting for I/O to complete.
1268The "softirq" line gives counts of softirqs serviced since boot time, for each
1269of the possible system softirqs. The first column is the total of all
1270softirqs serviced; each subsequent column is the total for that particular
12741.9 Ext4 file system parameters
1277Information about mounted ext4 file systems can be found in
1278/proc/fs/ext4.  Each mounted filesystem will have a directory in
1279/proc/fs/ext4 based on its device name (i.e., /proc/fs/ext4/hdc or
1280/proc/fs/ext4/dm-0).   The files in each per-device directory are shown
1281in Table 1-12, below.
1283Table 1-12: Files in /proc/fs/ext4/<devname>
1285 File            Content                                        
1286 mb_groups       details of multiblock allocator buddy cache of free blocks
12892.0 /proc/consoles
1291Shows registered system console lines.
1293To see which character device lines are currently used for the system console
1294/dev/console, you may simply look into the file /proc/consoles:
1296  > cat /proc/consoles
1297  tty0                 -WU (ECp)       4:7
1298  ttyS0                -W- (Ep)        4:64
1300The columns are:
1302  device               name of the device
1303  operations           R = can do read operations
1304                       W = can do write operations
1305                       U = can do unblank
1306  flags                E = it is enabled
1307                       C = it is preferred console
1308                       B = it is primary boot console
1309                       p = it is used for printk buffer
1310                       b = it is not a TTY but a Braille device
1311                       a = it is safe to use when cpu is offline
1312  major:minor          major and minor number of the device separated by a colon
1317The /proc file system serves information about the running system. It not only
1318allows access to process data but also allows you to request the kernel status
1319by reading files in the hierarchy.
1321The directory  structure  of /proc reflects the types of information and makes
1322it easy, if not obvious, where to look for specific data.
1330In This Chapter
1332* Modifying kernel parameters by writing into files found in /proc/sys
1333* Exploring the files which modify certain parameters
1334* Review of the /proc/sys file tree
1338A very  interesting part of /proc is the directory /proc/sys. This is not only
1339a source  of  information,  it also allows you to change parameters within the
1340kernel. Be  very  careful  when attempting this. You can optimize your system,
1341but you  can  also  cause  it  to  crash.  Never  alter kernel parameters on a
1342production system.  Set  up  a  development machine and test to make sure that
1343everything works  the  way  you want it to. You may have no alternative but to
1344reboot the machine once an error has been made.
1346To change  a  value,  simply  echo  the new value into the file. An example is
1347given below  in the section on the file system data. You need to be root to do
1348this. You  can  create  your  own  boot script to perform this every time your
1349system boots.
1351The files  in /proc/sys can be used to fine tune and monitor miscellaneous and
1352general things  in  the operation of the Linux kernel. Since some of the files
1353can inadvertently  disrupt  your  system,  it  is  advisable  to  read  both
1354documentation and  source  before actually making adjustments. In any case, be
1355very careful  when  writing  to  any  of these files. The entries in /proc may
1356change slightly between the 2.1.* and the 2.2 kernel, so if there is any doubt
1357review the kernel documentation in the directory /usr/src/linux/Documentation.
1358This chapter  is  heavily  based  on the documentation included in the pre 2.2
1359kernels, and became part of it in version 2.2.1 of the Linux kernel.
1361Please see: Documentation/sysctl/ directory for descriptions of these
1367Certain aspects  of  kernel  behavior  can be modified at runtime, without the
1368need to  recompile  the kernel, or even to reboot the system. The files in the
1369/proc/sys tree  can  not only be read, but also modified. You can use the echo
1370command to write value into these files, thereby changing the default settings
1371of the kernel.
13783.1 /proc/<pid>/oom_adj & /proc/<pid>/oom_score_adj- Adjust the oom-killer score
1381These file can be used to adjust the badness heuristic used to select which
1382process gets killed in out of memory conditions.
1384The badness heuristic assigns a value to each candidate task ranging from 0
1385(never kill) to 1000 (always kill) to determine which process is targeted.  The
1386units are roughly a proportion along that range of allowed memory the process
1387may allocate from based on an estimation of its current memory and swap use.
1388For example, if a task is using all allowed memory, its badness score will be
13891000.  If it is using half of its allowed memory, its score will be 500.
1391There is an additional factor included in the badness score: the current memory
1392and swap usage is discounted by 3% for root processes.
1394The amount of "allowed" memory depends on the context in which the oom killer
1395was called.  If it is due to the memory assigned to the allocating task's cpuset
1396being exhausted, the allowed memory represents the set of mems assigned to that
1397cpuset.  If it is due to a mempolicy's node(s) being exhausted, the allowed
1398memory represents the set of mempolicy nodes.  If it is due to a memory
1399limit (or swap limit) being reached, the allowed memory is that configured
1400limit.  Finally, if it is due to the entire system being out of memory, the
1401allowed memory represents all allocatable resources.
1403The value of /proc/<pid>/oom_score_adj is added to the badness score before it
1404is used to determine which task to kill.  Acceptable values range from -1000
1405(OOM_SCORE_ADJ_MIN) to +1000 (OOM_SCORE_ADJ_MAX).  This allows userspace to
1406polarize the preference for oom killing either by always preferring a certain
1407task or completely disabling it.  The lowest possible value, -1000, is
1408equivalent to disabling oom killing entirely for that task since it will always
1409report a badness score of 0.
1411Consequently, it is very simple for userspace to define the amount of memory to
1412consider for each task.  Setting a /proc/<pid>/oom_score_adj value of +500, for
1413example, is roughly equivalent to allowing the remainder of tasks sharing the
1414same system, cpuset, mempolicy, or memory controller resources to use at least
141550% more memory.  A value of -500, on the other hand, would be roughly
1416equivalent to discounting 50% of the task's allowed memory from being considered
1417as scoring against the task.
1419For backwards compatibility with previous kernels, /proc/<pid>/oom_adj may also
1420be used to tune the badness score.  Its acceptable values range from -16
1421(OOM_ADJUST_MIN) to +15 (OOM_ADJUST_MAX) and a special value of -17
1422(OOM_DISABLE) to disable oom killing entirely for that task.  Its value is
1423scaled linearly with /proc/<pid>/oom_score_adj.
1425The value of /proc/<pid>/oom_score_adj may be reduced no lower than the last
1426value set by a CAP_SYS_RESOURCE process. To reduce the value any lower
1427requires CAP_SYS_RESOURCE.
1429Caveat: when a parent task is selected, the oom killer will sacrifice any first
1430generation children with separate address spaces instead, if possible.  This
1431avoids servers and important system daemons from being killed and loses the
1432minimal amount of work.
14353.2 /proc/<pid>/oom_score - Display current oom-killer score
1438This file can be used to check the current score used by the oom-killer is for
1439any given <pid>. Use it together with /proc/<pid>/oom_score_adj to tune which
1440process should be killed in an out-of-memory situation.
14433.3  /proc/<pid>/io - Display the IO accounting fields
1446This file contains IO statistics for each running process
1451test:/tmp # dd if=/dev/zero of=/tmp/test.dat &
1452[1] 3828
1454test:/tmp # cat /proc/3828/io
1455rchar: 323934931
1456wchar: 323929600
1457syscr: 632687
1458syscw: 632675
1459read_bytes: 0
1460write_bytes: 323932160
1461cancelled_write_bytes: 0
1470I/O counter: chars read
1471The number of bytes which this task has caused to be read from storage. This
1472is simply the sum of bytes which this process passed to read() and pread().
1473It includes things like tty IO and it is unaffected by whether or not actual
1474physical disk IO was required (the read might have been satisfied from
1481I/O counter: chars written
1482The number of bytes which this task has caused, or shall cause to be written
1483to disk. Similar caveats apply here as with rchar.
1489I/O counter: read syscalls
1490Attempt to count the number of read I/O operations, i.e. syscalls like read()
1491and pread().
1497I/O counter: write syscalls
1498Attempt to count the number of write I/O operations, i.e. syscalls like
1499write() and pwrite().
1505I/O counter: bytes read
1506Attempt to count the number of bytes which this process really did cause to
1507be fetched from the storage layer. Done at the submit_bio() level, so it is
1508accurate for block-backed filesystems. <please add status regarding NFS and
1509CIFS at a later time>
1515I/O counter: bytes written
1516Attempt to count the number of bytes which this process caused to be sent to
1517the storage layer. This is done at page-dirtying time.
1523The big inaccuracy here is truncate. If a process writes 1MB to a file and
1524then deletes the file, it will in fact perform no writeout. But it will have
1525been accounted as having caused 1MB of write.
1526In other words: The number of bytes which this process caused to not happen,
1527by truncating pagecache. A task can cause "negative" IO too. If this task
1528truncates some dirty pagecache, some IO which another task has been accounted
1529for (in its write_bytes) will not be happening. We _could_ just subtract that
1530from the truncating task's write_bytes, but there is information loss in doing
1537At its current implementation state, this is a bit racy on 32-bit machines: if
1538process A reads process B's /proc/pid/io while process B is updating one of
1539those 64-bit counters, process A could see an intermediate result.
1542More information about this can be found within the taskstats documentation in
15453.4 /proc/<pid>/coredump_filter - Core dump filtering settings
1547When a process is dumped, all anonymous memory is written to a core file as
1548long as the size of the core file isn't limited. But sometimes we don't want
1549to dump some memory segments, for example, huge shared memory. Conversely,
1550sometimes we want to save file-backed memory segments into a core file, not
1551only the individual files.
1553/proc/<pid>/coredump_filter allows you to customize which memory segments
1554will be dumped when the <pid> process is dumped. coredump_filter is a bitmask
1555of memory types. If a bit of the bitmask is set, memory segments of the
1556corresponding memory type are dumped, otherwise they are not dumped.
1558The following 7 memory types are supported:
1559  - (bit 0) anonymous private memory
1560  - (bit 1) anonymous shared memory
1561  - (bit 2) file-backed private memory
1562  - (bit 3) file-backed shared memory
1563  - (bit 4) ELF header pages in file-backed private memory areas (it is
1564            effective only if the bit 2 is cleared)
1565  - (bit 5) hugetlb private memory
1566  - (bit 6) hugetlb shared memory
1568  Note that MMIO pages such as frame buffer are never dumped and vDSO pages
1569  are always dumped regardless of the bitmask status.
1571  Note bit 0-4 doesn't effect any hugetlb memory. hugetlb memory are only
1572  effected by bit 5-6.
1574Default value of coredump_filter is 0x23; this means all anonymous memory
1575segments and hugetlb private memory are dumped.
1577If you don't want to dump all shared memory segments attached to pid 1234,
1578write 0x21 to the process's proc file.
1580  $ echo 0x21 > /proc/1234/coredump_filter
1582When a new process is created, the process inherits the bitmask status from its
1583parent. It is useful to set up coredump_filter before the program runs.
1584For example:
1586  $ echo 0x7 > /proc/self/coredump_filter
1587  $ ./some_program
15893.5     /proc/<pid>/mountinfo - Information about mounts
1592This file contains lines of the form:
159436 35 98:0 /mnt1 /mnt2 rw,noatime master:1 - ext3 /dev/root rw,errors=continue
1595(1)(2)(3)   (4)   (5)      (6)      (7)   (8) (9)   (10)         (11)
1597(1) mount ID:  unique identifier of the mount (may be reused after umount)
1598(2) parent ID:  ID of parent (or of self for the top of the mount tree)
1599(3) major:minor:  value of st_dev for files on filesystem
1600(4) root:  root of the mount within the filesystem
1601(5) mount point:  mount point relative to the process's root
1602(6) mount options:  per mount options
1603(7) optional fields:  zero or more fields of the form "tag[:value]"
1604(8) separator:  marks the end of the optional fields
1605(9) filesystem type:  name of filesystem of the form "type[.subtype]"
1606(10) mount source:  filesystem specific information or "none"
1607(11) super options:  per super block options
1609Parsers should ignore all unrecognised optional fields.  Currently the
1610possible optional fields are:
1612shared:X  mount is shared in peer group X
1613master:X  mount is slave to peer group X
1614propagate_from:X  mount is slave and receives propagation from peer group X (*)
1615unbindable  mount is unbindable
1617(*) X is the closest dominant peer group under the process's root.  If
1618X is the immediate master of the mount, or if there's no dominant peer
1619group under the same root, then only the "master:X" field is present
1620and not the "propagate_from:X" field.
1622For more information on mount propagation see:
1624  Documentation/filesystems/sharedsubtree.txt
16273.6     /proc/<pid>/comm  & /proc/<pid>/task/<tid>/comm
1629These files provide a method to access a tasks comm value. It also allows for
1630a task to set its own or one of its thread siblings comm value. The comm value
1631is limited in size compared to the cmdline value, so writing anything longer
1632then the kernel's TASK_COMM_LEN (currently 16 chars) will result in a truncated
1633comm value.
16363.7     /proc/<pid>/task/<tid>/children - Information about task children
1638This file provides a fast way to retrieve first level children pids
1639of a task pointed by <pid>/<tid> pair. The format is a space separated
1640stream of pids.
1642Note the "first level" here -- if a child has own children they will
1643not be listed here, one needs to read /proc/<children-pid>/task/<tid>/children
1644to obtain the descendants.
1646Since this interface is intended to be fast and cheap it doesn't
1647guarantee to provide precise results and some children might be
1648skipped, especially if they've exited right after we printed their
1649pids, so one need to either stop or freeze processes being inspected
1650if precise results are needed.
16533.8     /proc/<pid>/fdinfo/<fd> - Information about opened file
1655This file provides information associated with an opened file. The regular
1656files have at least three fields -- 'pos', 'flags' and mnt_id. The 'pos'
1657represents the current offset of the opened file in decimal form [see lseek(2)
1658for details], 'flags' denotes the octal O_xxx mask the file has been
1659created with [see open(2) for details] and 'mnt_id' represents mount ID of
1660the file system containing the opened file [see 3.5 /proc/<pid>/mountinfo
1661for details].
1663A typical output is
1665        pos:    0
1666        flags:  0100002
1667        mnt_id: 19
1669The files such as eventfd, fsnotify, signalfd, epoll among the regular pos/flags
1670pair provide additional information particular to the objects they represent.
1672        Eventfd files
1673        ~~~~~~~~~~~~~
1674        pos:    0
1675        flags:  04002
1676        mnt_id: 9
1677        eventfd-count:  5a
1679        where 'eventfd-count' is hex value of a counter.
1681        Signalfd files
1682        ~~~~~~~~~~~~~~
1683        pos:    0
1684        flags:  04002
1685        mnt_id: 9
1686        sigmask:        0000000000000200
1688        where 'sigmask' is hex value of the signal mask associated
1689        with a file.
1691        Epoll files
1692        ~~~~~~~~~~~
1693        pos:    0
1694        flags:  02
1695        mnt_id: 9
1696        tfd:        5 events:       1d data: ffffffffffffffff
1698        where 'tfd' is a target file descriptor number in decimal form,
1699        'events' is events mask being watched and the 'data' is data
1700        associated with a target [see epoll(7) for more details].
1702        Fsnotify files
1703        ~~~~~~~~~~~~~~
1704        For inotify files the format is the following
1706        pos:    0
1707        flags:  02000000
1708        inotify wd:3 ino:9e7e sdev:800013 mask:800afce ignored_mask:0 fhandle-bytes:8 fhandle-type:1 f_handle:7e9e0000640d1b6d
1710        where 'wd' is a watch descriptor in decimal form, ie a target file
1711        descriptor number, 'ino' and 'sdev' are inode and device where the
1712        target file resides and the 'mask' is the mask of events, all in hex
1713        form [see inotify(7) for more details].
1715        If the kernel was built with exportfs support, the path to the target
1716        file is encoded as a file handle.  The file handle is provided by three
1717        fields 'fhandle-bytes', 'fhandle-type' and 'f_handle', all in hex
1718        format.
1720        If the kernel is built without exportfs support the file handle won't be
1721        printed out.
1723        If there is no inotify mark attached yet the 'inotify' line will be omitted.
1725        For fanotify files the format is
1727        pos:    0
1728        flags:  02
1729        mnt_id: 9
1730        fanotify flags:10 event-flags:0
1731        fanotify mnt_id:12 mflags:40 mask:38 ignored_mask:40000003
1732        fanotify ino:4f969 sdev:800013 mflags:0 mask:3b ignored_mask:40000000 fhandle-bytes:8 fhandle-type:1 f_handle:69f90400c275b5b4
1734        where fanotify 'flags' and 'event-flags' are values used in fanotify_init
1735        call, 'mnt_id' is the mount point identifier, 'mflags' is the value of
1736        flags associated with mark which are tracked separately from events
1737        mask. 'ino', 'sdev' are target inode and device, 'mask' is the events
1738        mask and 'ignored_mask' is the mask of events which are to be ignored.
1739        All in hex format. Incorporation of 'mflags', 'mask' and 'ignored_mask'
1740        does provide information about flags and mask used in fanotify_mark
1741        call [see fsnotify manpage for details].
1743        While the first three lines are mandatory and always printed, the rest is
1744        optional and may be omitted if no marks created yet.
1746        Timerfd files
1747        ~~~~~~~~~~~~~
1749        pos:    0
1750        flags:  02
1751        mnt_id: 9
1752        clockid: 0
1753        ticks: 0
1754        settime flags: 01
1755        it_value: (0, 49406829)
1756        it_interval: (1, 0)
1758        where 'clockid' is the clock type and 'ticks' is the number of the timer expirations
1759        that have occurred [see timerfd_create(2) for details]. 'settime flags' are
1760        flags in octal form been used to setup the timer [see timerfd_settime(2) for
1761        details]. 'it_value' is remaining time until the timer exiration.
1762        'it_interval' is the interval for the timer. Note the timer might be set up
1763        with TIMER_ABSTIME option which will be shown in 'settime flags', but 'it_value'
1764        still exhibits timer's remaining time.
1767Configuring procfs
17704.1     Mount options
1773The following mount options are supported:
1775        hidepid=        Set /proc/<pid>/ access mode.
1776        gid=            Set the group authorized to learn processes information.
1778hidepid=0 means classic mode - everybody may access all /proc/<pid>/ directories
1781hidepid=1 means users may not access any /proc/<pid>/ directories but their
1782own.  Sensitive files like cmdline, sched*, status are now protected against
1783other users.  This makes it impossible to learn whether any user runs
1784specific program (given the program doesn't reveal itself by its behaviour).
1785As an additional bonus, as /proc/<pid>/cmdline is unaccessible for other users,
1786poorly written programs passing sensitive information via program arguments are
1787now protected against local eavesdroppers.
1789hidepid=2 means hidepid=1 plus all /proc/<pid>/ will be fully invisible to other
1790users.  It doesn't mean that it hides a fact whether a process with a specific
1791pid value exists (it can be learned by other means, e.g. by "kill -0 $PID"),
1792but it hides process' uid and gid, which may be learned by stat()'ing
1793/proc/<pid>/ otherwise.  It greatly complicates an intruder's task of gathering
1794information about running processes, whether some daemon runs with elevated
1795privileges, whether other user runs some sensitive program, whether other users
1796run any program at all, etc.
1798gid= defines a group authorized to learn processes information otherwise
1799prohibited by hidepid=.  If you use some daemon like identd which needs to learn
1800information about processes information, just add identd to this group.
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